This invention relates to diagnostic equipment and, more particularly, to an apparatus useful in performing lung ventilation studies using radioactive gas.
Pulmonary ventilation studies have become a very useful diagnostic aid. Typically, a source of radioactive gas, such as radioactive xenon gas, is provided to a patient through a breathing tube. When the patient has inhaled the gas, a scintillation detector is used to obtain an image of the lung by detecting the presence of the radioactivity on a positional basis. In this manner, a physician can obtain useful information such as the degree to which inhaled gases are reaching the small passageways in the lungs.
Relatively elaborate and complex systems have been devised for delivering the radioactive gas to the patient and for receiving the exhaled gas and disposing of it safely. A number of considerations must be taken into account when designing such a machine. For example, when the patient is coupled to the gas delivery system, it is desirable that he be constrained to breathe only from the delivery unit, so provision is generally made for covering the mouth and nose with a mask such that ambient air cannot be inhaled. Since it is necessary for the patient to breathe during the setup and preparation periods, a source of oxygen is provided in the gas delivery system, the source being a part of the system which can be switched in, by appropriate valves. This can be disadvantageous, however, since the breathing of a higher than usual percentage of oxygen can temporarily affect lung function and disturb measurements which are taken shortly thereafter. Also, it is inconvenient and involves expense to provide a consumable source of oxygen in this manner.
A further problem with the prior art arises from the necessity of disposing of the radioactive gas without subjecting technical personnel to undue exposure or allowing exhausted gas to interfere with subsequent measurements. In most existing equipment provision is made for coupling the system's exhaust port to an external gas trap through which the exhaust gases are diverted to an appropriate conduit and eventually released outside the building. This is inconvenient in that it necessitates coupling to an external exhaust system which may or may not be available. Also, most existing gas traps for this purpose are not efficient enough to allow gas which has passed through them to exhaust into the room without possible harmful effects. These considerations are further complicated somewhat by the fact that the patient does not expel all of the radioactive gas in one breath. Rather, during a "washout" phase of operation, the patient breathes air or oxygen and the exhaust gas is only eliminated to the point desired after several breaths.
It is an object of this invention to overcome the prior art problems such as those set forth and to generally provide a combination delivery and exhaust system for radioactive gas ventilation studies.